If the Holy Roman Empire had won the Thirty Years War, what might Europe look like today?

The Catholic religion would probably dominated in Western Europe as rulers of the Holy Roman Empire were Catholics who were opposing the Protestant states and their supporters in Europe.

Explanation:

With the Thirty Years War the period of religious wars in Europe ended. This wars plagued Europe for a whole century until the peace treaty of Westphalia was signed. Holy Roman Empire was the biggest support to the Catholic church in the period of Reformation and Counter Reformation, but still wasn't able to prevent Protestantism to spread across Euroepe.